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A41.9ICD-10-CM

Sepsis, unspecified organism

BillableMaps to a high-scrutiny HCCNever reported with bacteremia NOSSeverity coded separately

How the code is built

A

Chapter

Certain infectious and parasitic diseases

41

Category

Other sepsis

9

Char 4

Organism not identified

Chapter

A00 to B99

Certain infectious and parasitic diseases

Block

A30 to A49

Other bacterial diseases

Category

A41

Other sepsis

Billable

Yes

Complete at 4 characters

Inclusion term

Septicemia NOS

The index default for sepsis with no organism

Excludes1

Bacteremia NOS, streptococcal, neonatal, puerperal

Never reported together with A41.9

Risk adjustment

HCC mapped

The septicemia, sepsis and shock category under CMS-HCC V28

DefinitionCode structureClinical pictureDocumentationDecision guideTabular listComparisonClaim contextRisk adjustmentDenialsSources

Key takeaways

  • A41.9 codes sepsis when the provider documented sepsis but no causative organism was identified
  • Assign it only when a provider states sepsis, since vital signs and cultures alone do not support it
  • The word septic in other phrases, such as septic emboli, does not license this code
  • Severity does not live in this code, so organ dysfunction and shock require additional codes
  • It is billable, and it maps to one of the most heavily audited risk adjustment categories
1Definition

What ICD-10 code A41.9 means

A41.9 is the ICD-10-CM code for sepsis, unspecified organism. It applies when a provider has documented sepsis, but the causative organism was never identified, whether cultures returned negative, were never drawn, or were still pending when the encounter closed.

The Alphabetic Index routes the unqualified term sepsis to A41.9, and septicemia NOS classifies here as well. What the code does not carry is severity. Sepsis, severe sepsis, and septic shock are the same code at this position, separated only by the codes reported alongside it.

Code

A41.9

Descriptor

Sepsis, unspecified organism

Chapter

Certain infectious and parasitic diseases

Block

Other bacterial diseases

Category

A41, other sepsis

Billable

Yes

Inclusion term

Septicemia NOS

Instructional notes

Code first for procedural and obstetric causes, with four Excludes1 conditions.

The descriptor has not changed since ICD-10-CM took effect, which makes A41.9 unusual among high-volume unspecified codes. The risk here is not stale wording in a template. It is a code that looks simple, carries more sequencing rules than almost anything else in the chapter, and sits in a risk adjustment category auditors examine first.

One word discipline matters more here than on any other code in this glossary. The adjective septic appears in many diagnoses that are not sepsis. Septic emboli, septic arthritis, and septic encephalopathy each classify on their own terms, and none of them permits A41.9. Follow the index entry for the documented phrase rather than reacting to the word.

2Code structure

Two decisions, only one of which lives in this code

The sepsis codes vary by organism. A41.9 is the end of that axis, the value assigned when nothing more specific is documented. The second decision a coder faces, severity, is not encoded in these characters at all.

Axis 1, organism

Character 4 and beyond

A41.0-

Staphylococcus aureus, split by methicillin susceptibility

A41.1, A41.2

Other specified and unspecified staphylococci

A41.3

Haemophilus influenzae

A41.4

Anaerobes

A41.5-

Gram-negative organisms, including E. coli, Pseudomonas, Serratia, Acinetobacter

A41.8-

Enterococcus and other specified sepsis

A41.9

Organism not identified — this code

This code

Streptococcal sepsis sits outside this category entirely, at A40.-, and is an Excludes1 rather than a sibling.

Axis 2, severity

Carried by a separate code

Sepsis without organ dysfunction

A41.9 alone

Severe sepsis, meaning acute organ dysfunction

A41.9, then R65.20, then each organ dysfunction

Septic shock

A41.9, then R65.21, then each organ dysfunction

This split is where the money is. A chart documenting acute kidney injury caused by sepsis reports at least three codes, and dropping the severe sepsis code understates the encounter without producing any edit that flags the omission. Note also that the septic shock code can never be the principal diagnosis, so the sepsis code always leads.

One gap in the code set worth knowing. ICD-10-CM has no code for viral sepsis. The A30 to A49 block classifies bacterial diseases, and sepsis with a specified organism not elsewhere classified indexes to A41.89. Official coding advice directs A41.89 as the best available option, paired with a second code identifying the agent, rather than forcing a bacterial code or defaulting to A41.9.

Which second code depends on what the record names.

Viral sepsis, virus not identified

A41.89 plus B97.89, other viral agents as the cause of diseases classified elsewhere

Sepsis due to a named virus

A41.89 plus the code for that virus

Sepsis secondary to viral syndrome

A41.89 plus the viral infection code the index reaches for syndrome

The convention behind this is the general rule that when an infection code does not identify the organism, a code from the bacterial and viral agent categories is added to supply it.

3Clinical picture

Clinical findings documented under A41.9

A record supporting this code describes a systemic response to infection, not a localized infection alone.

Temperature

Fever or hypothermia

Cardiovascular

Tachycardia, hypotension, poor perfusion, need for vasopressors

Respiratory

Tachypnea, hypoxia, increased work of breathing

Neurologic

Altered mental status, confusion, lethargy

Laboratory

Leukocytosis or leukopenia, elevated lactate, bandemia

Source

A documented or suspected infection site, such as urinary, pulmonary, skin, or abdominal

What distinguishes A41.9 from its siblings is the absence of an identified organism. What distinguishes it from a localized infection code is the provider's statement that the infection became systemic.

4Documentation

What the chart must show

  • The word sepsis, stated by the provider in the assessment, since clinical criteria alone do not permit code assignment.
  • The suspected or confirmed source of infection, documented as the site
  • Culture and sensitivity results, or a note that cultures were negative, pending, or not obtained
  • Vital signs, mental status, and laboratory values supporting a systemic response
  • Any acute organ dysfunction, explicitly linked to the sepsis rather than listed separately
  • Whether shock was present, using the word shock rather than describing hypotension alone
  • Present on admission status, since sepsis acquired after admission sequences differently
  • For a procedural, catheter, or obstetric cause, documentation of that relationship

Urosepsis is the single most common failure. It is not a codable term; it has no default code in the Alphabetic Index, and the Official Guidelines direct a query rather than an assumption. A coder who reads urosepsis and reports the urinary tract infection code has guessed, and one who reports A41.9 has guessed in the more expensive direction.

Note one asymmetry that helps rather than hurts. When septic shock is documented, and the word sepsis never appears, the sepsis code and the shock code may both be assigned, because septic shock cannot exist without sepsis.

5Decision guide

When to assign A41.9, and when not to

Sepsis, no organism identified

A41.9

Sepsis due to E. coli

A41.51

Sepsis due to MRSA

A41.02

Streptococcal sepsis

A40.-, never A41.9

Viral sepsis

A41.89, plus a code identifying the viral agent

Bacteremia, with no sepsis stated

R78.81, never alongside A41.9

Urosepsis

Not codable; query the provider

Sepsis with acute kidney injury caused by the sepsis

A41.9, then R65.20, then the kidney failure code

Septic shock, with or without the word sepsis

A41.9, then R65.21, then each organ dysfunction

Sepsis following a procedure

The postprocedural sepsis code first, then A41.9

Septic shock following a procedure

The postprocedural septic shock code in place of R65.21

Sepsis due to a central venous catheter

The catheter complication code first, then A41.9

Sepsis in a newborn

P36.-

Sepsis following delivery

O85

Septic emboli, septic arthritis, or septic encephalopathy

The code for that condition, not A41.9

Sequencing follows rules that pull in opposite directions. When sepsis is present on admission and caused by a localized infection, the sepsis code is sequenced first, and the localized infection follows. When a patient is admitted with a localized infection that progresses to sepsis afterwards, the localized infection leads. When sepsis develops from a procedure, catheter, or obstetric event, the cause is sequenced first, and A41.9 follows, because the category carries a code-first instruction naming exactly those situations. And when a non-infectious condition such as a burn or serious injury led to the infection and that condition meets the definition of principal diagnosis, the non-infectious condition is sequenced first.

Query rather than default when the note says urosepsis, describes organ dysfunction without linking it to the sepsis, or documents hypotension and pressors without using the word shock.

6Tabular list

Instructional notes at A41

Inclusion term

Septicemia NOS

Code first

Postprocedural sepsis, sepsis due to central venous catheter, sepsis during labor, sepsis following abortion, ectopic or molar pregnancy, sepsis following immunization, sepsis following infusion, transfusion or therapeutic injection

Excludes1

Bacteremia NOS (R78.81), neonatal sepsis (P36.-), puerperal sepsis (O85), streptococcal sepsis (A40.-)

Excludes2

Organism-specific sepsis classified elsewhere, including candidal (B37.7), gonococcal (A54.86), herpesviral (B00.7), listerial (A32.7), meningococcal (A39.2 to A39.4), and toxic shock syndrome (A48.3)

Use additional

A code from Z16.- to identify resistance to antimicrobial drugs, per the chapter-level note

The two Excludes notes behave in opposite ways, and confusing them is expensive. Excludes1 is a prohibition. A claim carrying both A41.9 and the bacteremia code is reporting two conditions the classification says cannot coexist. Excludes2 is a permission, so a patient with sepsis and a separately documented candidal infection may carry codes from both.

7Comparison

Codes frequently confused with A41.9

A41.0-, A41.5-, A41.8-

Descriptor

Sepsis due to a named organism

Use instead when

Cultures identified the causative organism

A41.89

Descriptor

Other specified sepsis

Use instead when

The organism is named but has no dedicated code, including viral sepsis

A40.-

Descriptor

Streptococcal sepsis

Use instead when

Streptococcus is documented, which is an Excludes1 at A41

R78.81

Descriptor

Bacteremia

Use instead when

Organisms are in the blood without a provider statement of sepsis

R65.20, R65.21

Descriptor

Severe sepsis without and with septic shock

Use instead when

Acute organ dysfunction is documented, reported after A41.9

R65.10, R65.11

Descriptor

SIRS of non-infectious origin, without and with acute organ dysfunction

Use instead when

The systemic response follows a non-infectious cause, and these are not reported alongside sepsis codes

P36.-

Descriptor

Bacterial sepsis of newborn

Use instead when

The patient is a newborn

O85

Descriptor

Puerperal sepsis

Use instead when

Sepsis follows delivery

A48.3

Descriptor

Toxic shock syndrome

Use instead when

Toxic shock is documented, which excludes sepsis NOS

B97.-

Descriptor

Viral agents as the cause of diseases classified elsewhere

Use instead when

Added alongside A41.89 for a viral cause

Z16.-

Descriptor

Resistance to antimicrobial drugs

Use instead when

A resistant organism is documented, added after the sepsis code

N39.0

Descriptor

Urinary tract infection, site not specified

Use instead when

The urinary source is coded alongside the sepsis code

8Claim context

Services commonly reported with A41.9

Sepsis is predominantly an inpatient diagnosis, and A41.9 anchors the septicemia diagnosis-related group family. Whether the encounter groups to the higher-weighted options depends on documented organ dysfunction and prolonged mechanical ventilation, both of which come from codes reported alongside A41.9 rather than from the code itself. Organism specificity also matters, since some organism-specific codes carry complication status that the unspecified code does not.

The present on admission indicator carries unusual weight here. Sepsis documented as present on admission behaves differently from sepsis acquired during the stay, both for sequencing and for hospital-acquired condition reporting.

On the outpatient and emergency side, A41.9 supports critical care time, emergency department evaluation and management, and observation services, each governed by its own time and documentation thresholds. Blood cultures and lactate testing are not among the twenty-three national laboratory determinations, so frequency and indication rules for those are set contractor by contractor. Sepsis also drives a national quality measure with its own bundle timing requirements, which is a documentation burden separate from coding.

9Risk adjustment

What A41.9 does to a risk score

The category pays well, and that is exactly why it is examined

A41.9 maps to the septicemia, sepsis, and systemic inflammatory response category under the current model, which reached full phase-in for payment year 2026. It is one of the higher-weighted categories in the model.

That weight makes it a standing audit target.

The category is among the most heavily scrutinized in Risk Adjustment Data Validation and Office of Inspector General reviews, precisely because the coefficient is high. The record has to substantiate the diagnosis with explicit provider documentation rather than screening criteria, supported by clinical indicators such as culture results, documented organ dysfunction, and treatment with antibiotics or vasopressors.

Screening criteria are not a diagnosis.

Official coding advice is explicit that a sepsis code is never assigned on clinical definitions, criteria, or clinical signs alone, and that code assignment rests on provider documentation regardless of which clinical criteria the provider used to reach it. So a chart where a sepsis alert fired, and a bundle was initiated, with no provider statement of sepsis in the assessment, does not support the code. This is the specific pattern reviewers look for, and it is common because the alerts are built to be sensitive rather than specific.

Report it in the year it occurs.

Risk adjustment does not carry a condition forward, and sepsis is an acute event rather than a chronic one, so the capture depends on the encounter where it was diagnosed and treated.

Verify the category and weight against the payment year.

A proposed increase to this category's coefficient is under consideration in a future model year, and category numbering changed between model versions, so an internal crosswalk built for an earlier year will not be reliable.

10Denials

Coding errors that cause denials

Coding A41.9 from clinical criteria or a sepsis alert without a provider statement

Query, since vital signs, lactate, and screening tools do not substitute for the diagnosis

Coding urosepsis as A41.9

Query for clarification, since the term maps to neither sepsis nor a urinary tract infection

Reporting A41.9 with bacteremia

Choose one, since the Excludes1 note prohibits both

Reporting A41.9 because the note says septic emboli or septic encephalopathy

Assign the code for the documented condition

Omitting R65.20 or R65.21 when organ dysfunction is documented

Add the severe sepsis code, then a code for each organ dysfunction

Sequencing the septic shock code as principal

Sequence the sepsis code first, since the shock code can never be principal

Reporting a severe sepsis code without the underlying infection code

Add it, since the severe sepsis codes are never reported alone

Adding a SIRS of non-infectious origin code alongside a sepsis code

Report the severe sepsis code alone, since the SIRS code is not needed

Sequencing A41.9 first when a procedure or catheter caused the sepsis

Sequence the cause first, per the code first instruction at A41

Using A41.9 when cultures identified the organism

Assign the organism-specific code, which may also change the severity classification

Defaulting viral sepsis to A41.9

Assign A41.89 with a code identifying the viral agent

Missing the antimicrobial resistance code

Add the applicable Z16.- code when a resistant organism is documented

11Sources

Where to verify A41.9

ICD-10-CM Official Guidelines for Coding and Reporting, Chapter 1 sepsis section

The sepsis, severe sepsis and septic shock sequencing rules in full, and the urosepsis query requirement

ICD-10-CM Tabular List at A41 and the chapter head

The code-first instructions, the four Excludes1 conditions, the Excludes2 list, and the chapter-level antimicrobial resistance instruction

ICD-10-CM Alphabetic Index at Sepsis and Septicemia

The routing of unqualified sepsis to A41.9, and the separate entries for the other septic conditions

CMS ICD-10 code page and the FY 2026 files

Current code files and the annual addenda

AHA Coding Clinic

The viral sepsis routing, the rule against coding sepsis from clinical criteria alone, and the published advice on organ dysfunction linkage

CMS Medicare Advantage rates and statistics

The current payment year model file, the category weight, and any proposed changes in the advance notice

Laboratory NCD list

Confirms blood cultures and lactate testing are not among the twenty-three national laboratory policies

Medicare Coverage Database

Search your contractor's determinations for critical care, observation, and emergency services reported with sepsis.

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Last reviewed August 2026

This page is a free reference for billing and coding teams and is not coding, legal, or clinical advice. Code selection depends on the documentation in the record and on the policy of the payer being billed. Verify every code, instructional note, and sequencing rule against the current ICD-10-CM files and the Official Guidelines for Coding and Reporting for the applicable date of service. ICD-10-CM is maintained by the CDC's National Center for Health Statistics and published by CMS. CPT is a registered trademark of the American Medical Association. TruCare is not affiliated with CMS, NCHS, the AHA, or the AMA.

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